Doctor for a suction roll particularly in paper machines

ABSTRACT

A doctor for a suction roll in a paper machine is intended to remove water from a suction roll. The doctor includes a doctor slat fitted against the surface of suction roll extending essentially over the entire width of the suction roll, as well as the doctor slat holder and loading devices. In the direction of rotation of the suction roll, there is a doctor blade, with a blade holder fitted to the doctor after the doctor slat. The doctor blade is arranged to remove the water lifted off the suction roll by the doctor slat.

TECHNICAL FIELD

The present invention relates to a doctor for a suction rollparticularly in paper machines, which doctor is intended to remove waterfrom the suction roll, and which doctor includes a doctor slat arrangedagainst the surface of the suction roll and essentially extending overthe entire length of the suction roll, together with the doctor slat'sretaining and loading members.

BACKGROUND OF THE INVENTION

A suction roll doctor, which removes water from the suction roll, isknown from FI patent application number 902910. The blade used in thedoctor is a doctor slat, which scrapes the film of water off the surfaceof the suction roll. In addition, the doctor slat creates a suction zonebehind itself, which also removes the water that has collected in thedrill holes and grooves of the suction roll. Part of the water raised byas the suction flows into a drainage tank beneath the suction roll, butthe rotation of the suction roll causes part of the moisture to travelback into the felt or similar. This causes the web or felt to becomesoaked, or at least causes unevenness in the moisture profile of theweb, felt, or paper.

A double doctor, in which an attempt has been made to improve the waterremoval capacity of the doctor by using two doctor blades, has also beenmanufactured for similar use. However, a conventional doctor bladecannot be used to achieve the suction effect of a doctor slat accordingto the invention, which can also suck the water out of the holes of thesuction roll. In addition, doctor blades operate in the desired manneronly over a certain part of the circumferential speed range of thesuction roll. In this case, when the speed of the paper machineincreases, both the water removal capacity of the doctor in question andthe result of the doctoring diminish substantially.

SUMMARY OF THE INVENTION

The invention is intended to create a new kind of doctor for a suctionroll particularly in paper machines, by means of which water can beremoved from the suction roll more effectively than previously.

A doctor for removing water from a suction roll in a paper machineincludes a doctor slat fitted against the surface of the suction rollextending essentially over the entire width of the suction roll, as wellas its holder and loading devices. In the direction of the rotation ofthe suction roll, there is a doctor blade and a blade holder fitted tothe doctor after the doctor slat and arranged to remove the water liftedoff the suction roll by the doctor slat. The angle between the lines ofcontact of the doctor slat and the doctor blade in relation to theimagined axis of rotation of the suction roll is 15-70°, preferably20-40°.

The doctor has a frame construction, to which holders of both the doctorslat and the doctor blade are fitted. The holder of the doctor slat isfitted detachably to the frame construction. The frame constructionincludes attachments corresponding to the blade holder of the doctorblade in the vicinity of the holder of the doctor slat.

The combination construction of a doctor according to the inventionactualizes the advantageous properties of the doctor, in practicecreating an excellent doctoring result. Simultaneously, a significantincrease in the total solids content is achieved. Besides water, fibresand filler substances are also removed from the holes in the suctionroll. This reduces the amount of loose material rotating with thesuction roll and also helps the suction roll's holes to remain clean.The doctor also evens the humidity in the area around the suction roll,as most of the water is recovered in a controlled manner. Thus, the web,felt, or similar do not become soaked, instead an even moisture profileis maintained. A doctor according to the invention can be used in allsuction roll positions. In addition, only small alterations are requiredto adapt the doctor to a very broad area of the auction roll's speedrange.

In the following, the invention is described in detail with reference tothe accompanying drawings, depicting some embodiments of the invention,in which drawings

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows side view of a doctor according to the invention,

FIG. 2 shows a side view of a doctor according to the invention, as partof an arrangement for removing water, fitted to a suction roll.

The doctor according to the invention, shown in FIG. 1, has two blades12 and 13, which are fitted to the frame construction 11 of the doctor10. Frame construction 11 is compact and is supported at both ends onbearings attached to the frame of the paper machine by means ofadjustable supports 14. The frame is shown by a dotted line. Ifnecessary, doctor 10 can be turned away from the surface of the suctionroll 15 by means of a turnbuckle 16 or similar. In FIG. 1, turnbuckle 16is fitted between a fixed bracket 17 and a supporting arm 18 attached tothe turning frame construction 11. However, turnbuckle 16 is mainly onlyused to adjust the position of the doctor 10. Blades 12 and 13 areloaded and released by means of holders 20 and 21, which are equippedwith conventional loading hoses 19 and 19′.

In the operating position in FIG. 1, blades 12 and 13 in doctor 10 actagainst the surface of suction roll 15, the actual suction sector beingon the opposite side of suction roll 15. Suction roll 15, the holes orgrooves in which are not shown in the drawing, rotates in the directionshown by the arrow. The water removed by the first blade 12 in thedirection of rotation of suction roll 15 is collected in a drainage tankbeneath suction roll 15. The water collected by the second blade 13 isled to a trough 22 formed in the frame construction 11, where it doesnot interfere with the operation of the first blade 12. The water isthen led from trough 22 to the drainage tank beneath suction roll 15.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, a doctor blade 13, which is as such known,is fitted to the doctor 10, behind the first blade 12, which in thiscase is a doctor slat, in the direction of rotation of suction roll 15.In the example, doctor blade 13 also includes a conventional bladeholder 21 and loading hoses 19′. This blade combination gives a betterdoctoring result than previously, especially when the circumferentialspeed of the suction roll is sufficiently high. In practice, the doctorslat 12 first removes the film of water from the suction roll 15 andthen creates a suction effect after it. This so-called foil effectalways arises when a suction roll rotates, but, as is known, significantsuction is only created once the circumferential speed of the suctionroll rises to a certain level. From this level onwards, the suctioneffect will usually increase, or at least remain the same. The foileffect sucks the water from the holes in the suction roll, which is thenremoved to trough 22 by doctor blade 13. Fibres and binders also risefrom the holes along with the water and are removed by doctor blade 13.A doctor according to the invention is so effective that the excessmoisture does not rotate with the suction roll. Thus, the suction rollalso functions more efficiently and re-wetting of the web or felt iseliminated.

Both doctor slat 12 and doctor blade 13 holders 20 and 21 are attachedto the frame construction 11 of the doctor, allowing both blades 12 and13 to be adjusted simultaneously in the doctor 10 installation. Inaddition, holders 20 and 21 are adapted to the frame construction 11 insuch a way that the angle α between the lines of contact of doctor slat12 and doctor blade 13 in relation to the imagined axis of rotation ofsuction roll 15 is 15-70°. Preferably, angle α is 20-400°. Doctor blade13 will then be able to move under the film of water raised by doctorslat 12 and the water will not have time to be sucked back into theholes. In addition, thanks to blades 12 and 13 being set close to eachother, the size of doctor 10 remains small. The doctor slat ispreferably made from plastic.

The holder 20 of doctor slat 12 is arranged to be attached to the frameconstruction 11 of doctor 10 in such a way that it can be detached. Inaddition, frame construction 11 includes attachment devices (not shown),corresponding to blade holder 21 of doctor blade 13, in the vicinity ofholder 20 of doctor slat 12. Thus, the same doctor can also be used inpaper machines that are classified as slow. In this case, it isjustified to install a doctor according to the invention, equipped witha conventional doctor blade, in a paper machine, even though the machineis of a so-called slow type. This allows the doctor to be rebuilt simplyin future speed-raising projects, by replacing the normal blade, whichhas acted as the first blade, with a doctor slat. The speed limit atwhich replacement is justified must be determined for individual cases.In principle, the suction effect of the doctor slat becomes significant,once the circumferential speed of the suction roll becomes sufficientlygreat.

To further improve the operation of the suction roll, it is preferableto arrange a doctor according to the invention as part of thearrangement shown in FIG. 2. The same reference numbers are used for thefunctioning parts. The arrangement according to FIG. 2 includespositive-pressure chamber 23, in which is fitted inside suction roll 15in the area of the doctor 10. Preferably, the positive-pressure chamber23 is located between blades 12 and 13, immediately after blade 12 inthe direction of rotation. The water-removing effect of the vacuumformed by doctor slat 12 is then reinforced by the positive pressuredischarging from the holes. Positive-pressure chamber 23 terminatesbefore the second blade, so that the operation of doctor blade 13 is notdisturbed by the flow of air. The arrangement empties the holes of thesuction roll more efficiently than before.

A suction roll doctor according to the invention can therefore beapplied over a broad range of the circumferential speed of a suctionroll, in all suction roll positions. In particular, the replacement ofthe doctor for different speed ranges is simple, which reduces costs. Inpractice, a significant increase in total solids content is achieved byusing the doctor. When the doctoring result is good, the moistureprofile after the suction roll is also more even, because the water thathas once been sucked from the web or felt does not return to the web orfelt. In this case, the veil of moisture surrounding the suction rollalso becomes thinner.

Although the invention has been described by reference to specificembodiments, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but that it have the full scope defined by thelanguage of the following claims.

What is claimed is:
 1. A doctoring device adapted for use with a papermachine suction roll having a suction roll axis of rotation, saiddoctoring device comprising: a doctor blade holder; a doctor blade fixedon said blade holder, said doctor blade having an edge against saidsuction roll and contacting said suction roll at an angle disposedrelative to a tangent of said suction roll at the point of contact; adoctor slat holder; a doctor slat connected to said slat holder, saiddoctor slat having an edge in urged engagement with said suction rollthrough a foil effect and contacting said suction roll at an angledisposed relative to a tangent of said suction roll at the point ofcontact; said doctor slat contact angle being smaller than said doctorblade contact angle; an angle defined by a first radius extending fromthe suction roll axis of rotation to the point of contact with saiddoctor blade and a second radius extending from the suction roll axis ofrotation to the point of contact with said doctor slat being in therange of 15 degrees to 70 degrees; said doctor blade beingcircumferentially disposed along said suction roll downstream of saiddoctor slat in a direction of rotation of said suction roll; and a framespacedly mounting both said doctor blade and said doctor slat; saidframe having a trough formed therein which collects water that has beendrawn onto the surface of said suction roll by said doctor slat.
 2. Thedoctoring device of claim 1 wherein said slat holder of the doctor slatis detachably fitted to said frame.
 3. The doctoring device of claim 1,wherein said doctor slat is trapezoidal in cross-sectional shape and abase of said doctor slat is in contact with said suction roll.
 4. Thedoctoring device of claim 1, wherein said doctor slat is made ofplastic.